Torsion spring devices



April 23, 1957 M. RUEGG ETAL 2,789,812

' TORSION' SPRING DEVICES Filed March 21, 1952 3m entors Gttomegs UnitedStates Patent TORSION SPRING "DEVICES Max -Ruegg, Detroit, and Von 'D.Polhemus, Franklin,

Mich, assignors to GemraLMotors Corporation, Detroit, lVficIn, acorporation of Delaware Application March *21,-152, Serial No; 277,881

.2 Claims. (Cl. 267- 57) "The present invention relates to t orsion typesprings and more particularly'to means for'improving'thefatigueresistance of bars or rods which aresubjected'totorsional stresses.

Compared with other'forms of springs, the torsion bar type of springoffers a very considerable advantage'in ease of fabrication, low cost,simplicity and maintenance. Theoretically, all that ,is required toutilize the spring characteristics of a given length of bar'is toanchorone end thereof and to provide a lever at the other end .to applytorque. Such spring could be manufactured ,at relatively low cost .ifbars of uniform thickness throughout the length thereof could beutilized. It has been found, however, that torsion bars of uniform cross.section have had a tendency to fracture prematurely, :usually in thearea wherethebar-emerges from the,anchor or 'lever bracket. Thistendency .is particularly ;.pronounced when the bars havebeen serratedor .splinedat each end and press fitted into the boresof the anchor andlever brackets. in experimenting with such cnstructionsit has been foundthat the stress concentration produced by ,serrating islocalized at thepoint of run-out of the serrations and-that this further increasesthetendency to fracture prematurely.

In the past attemptshavebeen madeto improve the fatigue resistancecharacteristic of bars by upsettingor otherwise-enlarging the endsofthebar in ordertoprovide a greater cross-sectional area at the point ofstress concentration. This methodof manufacture has tended to increasethe life of spring somewhat and,is used-to some extent commercially.Torsion bars constructedby this method have not proven to-beentirelysatisfactory because of the relatively high cost ofzmanufactureas compared with other types of structures, and'the-rate of productionis also relatively low because of the'forging operations requiredthereon. a

It is an object of the present invention to providea torsion bar ofuniform cross section which offers greatly improved resistance ;tofatigue at the points of stress concentration.

Another object is to provide a torsion bar of ,uniform cross sectionwhich is-highly re'sistantto fatigue, and which'is adaptable -'to any ofthe common methodsof attachment to-the associated members.

-A further object is'to provide a torsion bar which is susceptible toextremely-highspeed fabrication .anfdunusually low cost.

A still-further objectis to'provide a torsion bar type of spring whichis extremely :simpledn construction and highly efficient and durable inoperation.

-Other.- objects and novel features ofthe invention :will appearmore'fully hereinafterfrom thetollowing detailed description when takenin connection with the accompanyingfirawings. illustrating several.fOImS :-of t the invention of which:

Fig. 1 is a side elevation, partly in section, of a torsion bar sleevedin an anchor block and lever arm, showing the serrated or knurled endsterminating in a reduced ice portion which issubstantiallyjflush withtheinner faces of the anchorblock and lever arm.

-Fig. .2 is an enlarged sectional view taken substantially. alongline.2,2 of,Fig..1 and of Fig. 1 showing one form ofrknurling employed.

.Fig. 3is a view similar to ,Fig. .1 in which the recesses formed in the.torsion bar are disposed respectively, intermediate theendsOfthemounting bracket and lever arm.

Big. 4 is. a .view similar .to vFig. :3 showing va modified constructionwherein a second reduced portion at each end .is .substantially alignedwith .the inner .faces of .the respective anchorblockandlever arm.

.Fig. 5 is=a .viewsimilar to .Fig. .1.-showing another modifiedconstruction wherein .theends of 'the :bar are smoothandare t secured.against rotary movement in the anchorblockandin thelever-arrn bythreaded "means.

fiigro israiragmentary side :elevational view partly in section,:showing a-stillrfurther modification wherein thehiltiSDfaSQllfllfdCYOSS ,section having a circular groove disposednearthe inner face of 1 the support -therefor.

vFig. .7 .isra sectional .view of the bar shown in Fig. -6,thessectionbeingtakenzin a:plane passing through the annular groove inthebar.

,Fig. .8.,is. a view similar-toFig. 6:showing'a'sti1l furthermodification wherein .a torsion bar of polygonal construction isemployed, and

Fig.19is a sectionalr-end view of the-bar shown in Fig. Sttakenthrough-.theiplaneof the circular groove provided therein.

Referringmow .to the drawings the numeral '2designates.a.torsionrbar-secured atone end 4 in an anchor bracket 12and-at the other end .6 inalever bracket 14. Both-ends 4:.and *6 of bar2 .are provided with longitudinally extending knurled portions i6 whichmay be-formed .thereon by a thread-rollingmachine or othersuitable-device. In Fig. .Z-the cross "sectional form of the iknurls16,-is illustrated on an enlarged-scale. The anchor bracket '12 andlever bracket 14 are provided with bored apertures :8 and'10respectively, into which theknurled'end'portions :16 'of bar :2 arepressed. Apertures .8 i and :10 :are'usually bored to a diameterslightly less than the .pitch diameter of the knurled end portions 16 ofthe '-bar,;i-n orderlto obtain an interlock of ample torque capacity.:Tosecure a;more favorable distribution of stresses in accordance withthe invention, tapered annular grooves 32 are formed on the barZ at the:run-out of :the :longitudinally extending knurled portions .16 and thebar 2 ispressed into the bored apertures'il'and 10 0f *the "anchor'andlever brackets 12 and 14 asuflicientdepth.to'position the annulargrooves 32 substantiallyflush with :theinner faces 34 and '36respectively,;off the-said anchorzand lever'brackets. Tests haveshown=that'by'disposing the annular grooves 32 in thismannera.substantial reduction in stress concentration isobtained,thereby vincreasing the bar'life by-more than fifty-percent. inaddition to stress concentration where thetbarfZ emerges from 'thebrackets 12 and '14, it has been ifound that fknurling 'or otherwisedeforming the ends of :the 'bar :in'duces "additional stress Iconcentration which'isilo'calized-atithe run out of such knurling. Itwill therefore"be=-apparent that in Fig. "1 the annular grooves 32 are:formed on the bar 2 and positioned with respectthe anchor andleverbrackets I2and'1'4 in such a smannerzas "to relieve =inherent'stress concentrations occasioned :by the rigid attachment of the bar"to the brackets as well as stresses induced by'knurling the endofithessaid bar.

,A mddificationuofithe s'tructureshownin Fig. 1 is illustrated in Fig.3. In this construction a bar 2 has provided at the opposite ends 4 and6 thereof a relatively short longitudinally extending knurled portion 16and an annular groove 32 at the run-out of each of said knurledportions. The opposite ends 4 and 6 of bar 2 are pressed into the anchorbracket 12 and lever bracket 14 a sufficient distance to place theannular grooves 32 in a plane intermediate the inner and outer faces 34and 35 of said anchor bracket and the inner and outer faces 36 and 37 oflever bracket 14. Tests have shown that the bored apertures 8 and 10 ofthe anchor and lever brackets 12 and 14 overlap and grip the smoothportions 38 of the bar 2 ahead of the annular grooves 32 and tend torelieve the grooved portions 32 of the full torque load, thereby furtherimproving the distribution of stresses and materially improving the barlife.

Fig. 4 shows a still further modification of the structure shown inFig. 1. In this construction also the anchor bracket 12 and leverbracket 14 are pressed on the ends 4 and 6 of the bar 2. Each end 4 and6 of the bar 2 shown in Fig. 4 is provided with short knurled endportions 16 and a pair of spaced apart annular grooves 32 and 49. Thegrooves 32 are formed at the run-out of each of the knurls 16 and occupya plane intermediate the inner and outer faces 34 and 35 of the anchorbracket and the inner and outer faces 36 and 37 of the lever brackets14. The grooves 40 occupy planes substantially flush with the innerfaces 34 and 36 of the anchor and lever brackets 12 and 14,respectively. In this modification the annular grooves 32 relieve stressconcentration induced by knurling while the grooves 40, shown here intapering form, tend to relieve excessive stresses occurring in thepress-fit area of the smooth portions 39 of the bar 2 between thegrooves 32 and 40.

Fig. shows a still further modification comprising a torsion bar 2 ofsubstantially uniform cross section throughout and having smoothsubstantially cylindrical end portions 4 and 6. The end portions 4 and 6of bar 2 are press fitted into bored apertures 8 and of the anchor andlever brackets 12 and 14, respectively, and held securely therein bythreaded members 41. Near each end of the bar 2 there is provided anindentation 42 into which the tapered end 43 of the threaded member 41is firmly seated to provide a rigid connection of ample torque capacity.Annular grooves 32 are formed on each end of the bar 2 inwardly of theindentations 42 and occupy a plane substantially flush with the innerfaces 34 and 36 of the anchor and lover brackets 12 and 14,respectively. It will be apparent that the threaded members 41 providefor axial positioning of the annular grooves 32 with respect the innerfaces of the anchor and lever brackets 12 and 14, respectively, as wellas providing a rigid interlock between the bar and the said anchor andlever brackets.

Figs. 6 and 7 show a still further modification. In this constructionthe numeral 44 designates an anchor bracket having a substantiallysquare aperture 45 provided therein. A substantially square torsion bar46 having a stress relieving annular groove 32 formed near one end ispressed into the aperture 45 to obtain rigid engagement between the bar46 and the anchor 44. In this embodiment the groove 32 is positioned ina plane substantially flush with the inner face 42 of the anchor bracket44. Since the end portion of the bar 46 requires no alteration toprovide for rigid engagement, it will be apparent that this embodimentwill substantially reduce the cost of fabricating the bar. The oppositeend of bar 2 may be of similar construction and fitted into asubstantially square opening provided in a lever bracket (not shown).Tests on this type of bar have indicated that stress concentrations aresubstantially reduced by an annular groove 32 therein having a crosssectional diameter substantially equal to the minimum cross section ofthe bar, as shown particularly in Fig. 7.

Figs. 8 and 9 illustrate a modification of the structures shown in Figs.6 and 7 in which a torsion bar 47 of polygonal cross section is pressfitted into an anchor bracket 48 having an aperture 49 of similarpolygonal shape. A stress relieving annular groove 32 is formed on thebar 47 near one end thereof. The end 50 of the bar 47 is axiallyadjusted into the aperture 49 so that the groove 32 occupies a planeadjacent the inner face 51 of the anchor bracket 48 and is preferably ofa cross sectional diameter equivalent to that of the minimum width ofsaid bar as illustrated in Fig. 9. The other end of the bar 47 may besimilarly constructed and press fitted into a polygonal opening in alever bracket (not shown).

While the present invention is particularly suitable in conjunction withtorsion bars of substantially uniform cross section, it is to beunderstood that the advantages are equally applicable to bars of varyingcross section, and the several illustrations therefore are not intendedas defining limits of the invention. It therefore is to be understoodthat it is intended to limit the invention only by the scope of theclaims which follow.

We claim:

1. In a device of the class described, the combination of an anchorbracket, a lever bracket, said brackets having opposed faces, each ofsaid brackets having a bore formed therein, a torsion spring member,said member having an elongated intermediate portion of circular crosssection and terminal end portions of circular cross section, said endportions and said intermediate portion being equal in diameter, knurlmeans on said end portions,

stress relieving means formed on said bar at the junctures of saidintermediate portion and said knurl means, said last mentioned meanscomprising tapered annular grooves in said bar, said taper divergingtoward said intermediate portion of said bar, said knurl means beingpress fitted into the bores of said anchor and lever bracket to positionsaid grooves in external flush relation with the opposed faces of saidbrackets.

2. In a device of the class described, the combination of an anchorbracket and a lever bracket having opposed faces, each of said bracketshaving a bore formed therein, a torsion spring member, said memberhaving an elongated intermediate portion of circular cross section andterminal end portions of circular cross section, said end portions andsaid intermediate portion being equal in diameter, means formingserrations on said end portions, said serrations being adapted for pressfitted gripping engagement with said bores, stress relieving meansformed on said bar at the junctures of said intermediate portion andsaid serrations, said last mentioned means comprising annular grooves insaid bar, said grooves having one wall generally transverse to the axisof said bar and another wall inclined with respect to the axis of saidbar, said end portions being press fitted into the bores of said anchorand lever bracket to position the transverse walls of said grooves inflush relation with the opposed faces of said brackets.

References Cited in the file of this patent UNITED STATES PATENTS1,370,073 Utz et a1. Mar. 1, 1921 1,790,737 Alborn Feb. 3, 19312,016,753 Patzig Oct. 8, 1935 2,082,509 Rabe June 1, 1937 2,133,739Collins Oct. 18, 1938 2,453,117 Buckendale Nov. 9, 1948 2,588,018Lauenstein Mar. 4, 1952 FOREIGN PATENTS 415,993 Italy Nov. 12, 1946469,134 Great Britain July 20, 1937 OTHER REFERENCES Product Engineeringof January 1947, page 119. Publication On Variable Stress by J. SelwynCaswell.

